The present invention relates to the fabrication of insulating glass units for windows, and more particularly to a system for fabricating muntin bars used in the construction of insulating glass units.
Windows constructed from multiple glass panes utilized xe2x80x9cmuntinsxe2x80x9d or xe2x80x9cmuntin barsxe2x80x9d to secure the edges of the individual glass panes within the window sash. In many windows, muntins formed distinctive grid patterns that are associated with architectural styles of buildings containing the windows.
Modern windows formed by insulating glass units utilize single glass lights separated by an insulating dead air space. Where a particular architectural xe2x80x9clookxe2x80x9d is desired, a grid of muntin bars is fixed in the dead air space between the glass lights to simulate a multipane window. Typical muntin bars for insulating glass units are formed from decoratively coated interfitted metal tubes. The grids are anchored to the insulating glass unit periphery.
Constructing muntin bar grids for insulating glass units has been a labor intensive process. As a consequence, manufacturing such units, and thus windows formed by the units, has been costly and inefficient. Some efforts to mechanize the manufacture of muntin grids have been made. For example, machines for notching lengths of preformed tubular muntin bar stock at predetermined locations have been proposed. The muntin bar stock is cut into lengths for use in forming a grid for a given size insulating glass unit. The cut muntin bar stock is then fed into the notching machine and notches are formed at predetermined locations along each length. The grids are assembled by hand by interfitting the respective muntin bars at the notches.
The muntin bar stock is produced by roll forming decoratively coated sheet material such as aluminum or steel, in a known manner. Various sizes of the sheet material are used to form different size muntin bar stock. The roll forming machine has a series of rolls configured to form sheet material into elongated tubular muntin bar stock. A window manufacturer purchases the muntin bar stock size(s) needed to produce insulating glass units and, as described above, cuts the stock into lengths that are notched and assembled into grids for incorporation into the insulating glass units.
Conventional muntin bar constructions suffer from several drawbacks with respect to cost and efficiency. For example, insulating glass unit manufacturers are required to purchase and maintain an inventory of tubular muntin bar stock. In some instances, several different muntin bar stock sizes and colors are inventoried to produce grids for various insulating glass units. This necessitates dedicated muntin bar stock storage space and increases costs associated with inventory. In addition, the muntin bar stock must be cut into lengths the size of which depends on the size of the insulating glass units being manufactured. While dedicated machinery may be used to cut the stock, a machine operator is still required to perform at least some hand measurements in order to produce correctly cut-to-length muntin bars. Moreover, cutting the muntin bar stock frequently results in unusable scrap.
The cut-to-length muntin bars are then fed to a notching device to form notches that will be located at the muntin bar intersections. Although some machinery may be specialized to notch the bars for forming grids, the muntin bars typically must be manually handled to produce correctly sized muntin bars with properly located notches. As a result, conventional construction of muntin bars and muntin bar grids requires the operator to perform a series of fabricating steps, thereby increasing the difficulty and cost associated with such construction. The handling and notching procedures may also result in damage to the muntin bar finish and denting, or creasing.
The present invention provides a new and improved system for fabricating muntin bars which is so constructed and arranged that muntin bars are quickly and efficiently formed from sheet material, notched or otherwise formed to permit subsequent attachment in a grid, and then cut to length without requiring significant handling or mentation on the part of the individual fabricating the muntin bars. The invention provides a method and apparatus for continuously producing notched muntin bars from sheet stock; thus, a manufacturer is able to store coils of sheet material rather than a supply of precut tubular muntin stock. Also, production of the muntin bars is automatically controlled to allow muntin bars to be custom formed for specific orders.
The present invention concerns method and apparatus for making a contoured muntin bar. A strip of sheet material having a finished surface on at least one side is unwound from a supply and fed along a strip travel path to a punch station. At the punch station a ribbon punching mechanism punches the ribbon at a precisely predetermined locations along the ribbon to form one of a plurality notch patterns that define a portion of a contoured muntin bar.
Downstream from the punch station the ribbon is fed through a forming station having a succession of forming rolls that bend the ribbon and form a generally closed cross-sectional tube. The rolls bend the strip in stages to produce a muntin bar tube having a contoured shape with raised sides that provide an attractive appearance to the muntin grid made from the contoured muntin bars.
The closed cross-section tube is routed from the forming station to a cutting station. At the cutting station an endmost muntin bar is cut from the tube at a precisely predetermined location by cutting the tube along a cut line that is defined by the notch patterns. Sensors monitor the progress of the fabrication of muntin bars and communicate the sensed status to a programmable controller which co-ordinates all processing steps.
A second of the notch patterns creates a mitred end to the muntin bars. In response to sensing a notch pattern for forming a mitred bar end, the controller initiates the clamping an end of the muntin tube prior to severing an endmost muntin bar. After the severing step, the severed muntin bar is moved away from the muntin tube to which it was previously attached to widen a gap between the severed muntin bar and the muntin tube. The mitred ends of the severed muntin bar and the muntin bar tube that are spaced apart by the gap are then finished by moving a high speed router bit specially configured to shape the ends through this widened gap.
After an endmost bar is severed the process has produced a tubular muntin bar made up of an elongated tube having two mitred ends, two flat ends or one mitered end and one flat end. The mitred ends include muntin bar portions that fit over mid portions of other muntin bars to form a part of a grid. The flat ends form outer bounds of a completed muntin bar grid for contacting a window spacer frame.
The cross section of a completed muntin bar defines a perimeter that encloses an area having the general shape of a cross. The cross-shaped area defined by the perimeter of the formed muntin bar has two relatively narrow top and bottom legs and two relatively wide side legs. The length of the top and bottom legs is the same and the length of the two side legs is the same. The width of each leg tapers down along its length. A seam is formed at the end of one of the legs where two edges of the material used to form the tube meet. No welding of the seam is required after severing of the muntin bar. The severed bar can immediately be assembled into an attractive ready to install muntin bar grid.
Practice of the invention results in faster production of contoured muntin bars when compared to prior art production speeds. Using the apparatus and method of the disclosed invention, one person can make and assemble 1000 grid units during an eight hour shift compared to approximately 200 units when using fabrication techniques of the prior art. The cost per foot of muntin bar produced is also lower. The cost in making the contoured muntin bars using the invention is less than half the cost of making them with prior art apparatuses and the quality is better. More specifically, the invention produces higher quality, virtually seamless bars with precision cuts where the bar engages the window spacer frame and miters the muntin bars where they engage cross bars of the grid. The invention facilitates xe2x80x9cjust in timexe2x80x9d manufacturing since the bars that make up a grid can be programmed into a controller and produced by the operator as other grids are being made. The controller optimizes the use of materials. The controller makes muntin bars for each grid in turn and then begins producing muntin bars for a subsequent grid based on a program of jobs programmed by the user. Excess payout of strip material is avoided and practice of the invention has reduced scrap material by at least 10 percent.
These and other objects, advantages and features of the invention will become better understood from the detailed description of a preferred embodiment of the invention which is described in greater detail in conjunction with the accompanying drawings.